Today the watch totaly crashed by starting a run.
Hard reset does not work, i see only the triangel.
was updates.
All,
We are aware of the disruption of devices displaying a blue triangle when starting a GPS activity. Holding the power button until the unit powers off may or may not restore functionality temporarily…
All,
Thank you very much for your patience as we worked on this issue. Please see the steps from My Garmin Device Will Not Boot Past the Start Up Screen for a resolution. If you already performed the steps…
Although appreciated, it's completely absurd the only guidance we have are some other users suggesting button combinations to get these devices to power back on but not resolve this issue. Where is…

Yep, bricked Forerunner 255. I started a walk and flashing triangle. A soft reset does nothing.
I'm not using beta firmware; had an update about a week ago.
Additionally the Connect app on my phone…
Master reset works. But it will reset your max heart rate. After the first run it updated the max heart rate to the „correct one“ (i.e. the one i had before the master reset).
so my training zones were a off, but now the its all fine again.
of course when you do a master reset you also habe to pair the device again and do the whole setup, like garmin pay, load courses for navigation etc.
I did the hard reset on a 255M and it worked for me. I synced it with the Garmin Connect app on my iPhone. I was able to start an activity after the reset with no issues. It seems that the trick for now is not to sync with Garmin Express on your computer but with Garmin Connect on your phone.